1. Field of the Invention
This invention relates to a corrugated heat pipe for conducting terrestrial heat onto the surface of the ground for utilizing it for melting snow, power generation and so forth.
2. Description of the Related Art
Heretofore, a corrugated heat pipe is used to conduct terrestrial heat onto the ground surface from hot water in the ground by heat conduction, without depriving the ground of hot water or steam. Several tens or hundreds rigid heat pipes of steel or alloy steel, each, for example of 10 long are laid out at the installation site and connected one by one, using male and female screws, to obtain a single long heat pipe which is then inserted in the ground. A pipe having this structure can sufficiently withstand the hanging load and also radial pressure externally applied to it is the depth of the ground. This method of installation, however, has problems as regards operability. The operation performed when the pipes are connected on the installation site encounters great diffuculties depending on status and evironments of the installation site. Nevertheless, the installing method is used in which the pipes are connected on the installation site. This is because if a single long steel or alloy steel heat pipe is completed in factory, it can not be transported to the installation site, because of its size and weight. There has been a proposal for improving the operability on the site. This proposal is to provide a heat pipe having flexibility and reduced wall thickness. If a single long corrugated heat pipe having flexibility and reduced wall thickness is completed in factory, it can be readily transported to the installation site by winding it onto a drum. In addition, the flexible material is very light in weight compared to steel or alloy steel. The flexible heat pipe is used as thermal siphon and is buried in the ground by inserting it into the ground to a depth of 200 to 5,000 m.
However, this method has the following problems.
Since a pipe as long as several hundred to several thousand meters is buried such that it is suspended at the ground surface into the ground, it is subject to elongation due to its own weight, resulting in flattening of its corrugated outer peripheral surface or breakage of it. The flattening of the corrugated outer peripheral surface leads to fluctuations of the heat transfer characteristics in the longitudinal direction.
When in the ground, the pipe is liable to be crushed due to a radial external pressure applied to it. Generally, the pipe experiences as high pressure as 0.12 kg/cm.sub.2 multiplied by the depth in meters. In the depth of several thousand meters, the pipe experiences an external pressure of several hundred kg/cm.sup.2, so that it will be crushed if it has reduced wall thickness.
To solve the above problems, in the case of a power cable used for a mining pit, a steel wire is wound closely helically on the entire outer periphery of the inner sheath, and the helically wound steel wire is covered by an outer sheath of vinyl or polyethylene. In this case, however, the handling of a hanger at the top of heat pipe is a very difficult operation. In addition, when the heat pipe provided with this means is insertedly buried in the ground, its flexibility is spoiled due to its very great weight. Further, the use of the vinyl or polyethylene sheath gives rise to the problems of the resistance against the terrestrial heat at high temperatures of 200.degree. C. or above and reduction of the heat conductivity.